Perhaps you should try some spelling variations:
hieu van » thien van, lieu va, hieu ve
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
xuc va » duc va, luc va, xac va
tuc va » thuc va, truc va, tuc xa
vi cua » vai cua, di cua

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky nang xa hoi. ((hieu van) OR (hieu va)) cac ((xuc va) or (tuc va)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang xa hoi. ((hieu van) OR (hieu va)) cac ((xuc va) OR (tuc va)) hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang xa hoi. ((hieu van) OR (hieu va)) cac ((xuc va) or (tuc va)) hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang xa hoi. ((hieu van) OR (hieu va)) cac ((xuc va) or (tuc va)) hanh vi cua tre*.